"They will match the regular price," Almond said. "But if your car takes midgrade or premium, its much higher."

Spread between grades much higher

Many stations, including many Shell stations, now have only the price of regular showing on their new digital signs.

You have to pull up to realize that while regular is $3.71 (competitive with other nearby stations), midgrade is $3.86 and premium $4.01, a much wider spread than the old pricing.

The gas station Almond was referring to would not comment, but Shell Oil tells the tech blog CNET that it's premium fuel, V-Power, is costlier than other brands "due to its lower friction and extra cleaning agents."

GasBuddy.com, meantime, says refineries are producing less premium gas nowadays, so the price is up based on supply and demand.

Almond just wishes stations would post all their prices, and says drivers need to be on guard.

What you can do

My advice? If your car suggests premium, check with your handbook, and your dealer's service department, to see if it's required or just recommended.

You may be able to drop down a grade, saving a few cents per gallon, so you don't waste your money.

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